Thanks

All electric heaters are 100% efficient. There is no difference in operating cost between these heaters. None.

That said, don't use one that has a glowing wire - they simply are not safe. Portable electric heaters have a bad safety reputation in general. I would recommend the oil filled as well.

Keep in mind:

One heater will max out a 15 amp circuit all by itself. You can't operate anything else on that circuit. Not a lamp, computer, or anything.

For that reason, you also can't operate two heaters on one circuit.

Do not use extension cords of any type.

Keep the heaters away from drapes, sheets, etc.

Make sure your smoke detectors are working.

Heat pumps are the most efficient way to heat, but I've not come across a portable model yet. That said, if you're planning on doing this regularly it might make sense to have mini-split heat pumps installed in the bedrooms. You would also then be able to do the reverse in the summertime -- cool only the rooms you're in.

Generally, heat pumps put out 3x the heat for the same amount of watts compared to a portable heater. So if your portable heater needs to run for about 5 hours/day, it'd use the same amount of electricity that a heat pump would in 15 hours. Adds up over time.

I was looking at upgrading my A/C with a heat pump but I live in NE PA and we have cold winters which make HP not the best choice. I looked at a Hallowell which claim to be efficient at low temps but they are too new and have none installed in my area. I don't want to be the new kid on the block.